At present, hydrogen peroxide is manufactured almost exclusively for commercial purposes by using alkylanthraquinone as working material. In the alkylanthraquinone process, a working solution prepared by dissolving alkylanthraquinones (alkylanthraquinone and tetrahydroalkylanthraquinone) in an organic solvent is first reacted in the presence of a catalyst with hydrogen gas to produce alkylanthrahydroquinone. When the alkylanthrahydroquinone is oxidized by air or oxygen gas back to alkylanthraquinone, hydrogen peroxide is produced. Thus produced hydrogen peroxide is extracted with water, separated, and then purified. The working solution separated through extraction is recycled for reduction, oxidation and extraction. This autoxidation cycle using alkylanthraquinone is well known in the literature (Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., 1993, Vol. 13, pp. 961-995).
In the autoxidation cycle, the working solution is recycled repeatedly, during which some of the alkylanthraquinone in the working solution is slowly converted into tetrahydroalkylanthraquinone and concentrated in the working solution. The composition and content of the working solution greatly affect the productivity of hydrogen peroxide, reaction rate, easiness of process operation, and production of inert ingredients from side reactions of alkylanthraquinone.
There have been many suggestions with respect to the composition of the working solution, i.e., the kind and proportion of alkylanthraquinones.
Korean Patent Publication No. 10-2008-0007102 discloses a method for preparation of hydrogen peroxide using a working solution comprising a 2:1 to 8:1 (molar ratio) mixture of 2-alkylanthraquinone (AQ) and 2-tetrahydroalkylanthraquinone (THAQ), in which 55-90 mol % of the alkyl of the total quinones is amyl and the remaining 10-45 mol % of the alkyl is ethyl. Although this patent aims at preparation of hydrogen peroxide with low impurity content, the productivity of hydrogen peroxide is not so high because the solubility of the reduced form alkylanthrahydroquinone (AHQ) is lower than that of tetrahydroalkylanthrahydroquinone (THAHQ). Further, a higher proportion of alkylanthraquinone than tetraalkylanthraquinone during the reduction results in slow hydrogenation reaction rate, which, in turn, leads to loss of alkylanthraquinone through side reactions.
U.S. Pat. No. 6,153,169 uses 2-ethylanthraquinone (EAQ) and 2-amylanthraquinone (AAQ) as well as 2-(4-methyl-3-pentenyl)-anthraquinone (IHEAQ) or 2-(4-methylpentyl)-anthraquinone (IHAQ) as working material. One of the conditions required for quinone as working material is that it should be commercially available and inexpensive. However, as mentioned also in the patent, IHEAQ and IHAQ are commercially unavailable and should be synthesized for use. Further, the cost of the raw material is much higher than that of EAQ or AAQ.
U.S. Pat. No. 6,524,547 suggests the use of a working solution comprising a mixture of 2-ethylanthraquinone and 2-amylanthraquinone, wherein the content of 2-amylanthraquinone is 10-55 mol % and the molar ratio of tetrahydroalkylanthraquinone to alkylanthraquinone is at least 1:1. However, because of the high proportion of 2-ethylanthraquinone, the solubility of alkylanthraquinone and alkylanthrahydroquinone is low and reaction rate is slow. Due to the low solubility and slow reaction rate, it is difficult to improve the productivity of hydrogen peroxide.
WO 95/28350 discloses a method for preparation of hydrogen peroxide using an all-tetra system working solution consisting of 2-tetrahydroethylanthraquinone and 2-tetrahydroamylanthraquinone. However, the productivity of hydrogen peroxide is not high because the solubility of tetrahydroalkylanthraquinone is lower than that of alkylanthraquinone. Further, a harsh reaction condition is required during the oxidation process because the oxidation reaction rate is retarded. In addition, tetrahydroalkylanthraquinone is not commercially available, and so it should be synthesized through an additional process.
Japanese Patent Laid-open No. Hei 6-191803 discloses a method for preparation of hydrogen peroxide using a working solution comprising 3:1 to 6:1 (molar ratio) of 2-amylanthraquinone (AAQ) and 2-tetrahydroamylanthraquinone (THAAQ). However, because of high alkylanthraquinone content, this method is associated with the problem of loss of alkylanthraquinone caused by side reactions of the alkylanthraquinone during reduction. Further, the productivity of hydrogen peroxide is not high since the solubility of reduced alkylanthrahydroquinone (AHQ) is less than that of tetrahydroalkylanthrahydroquinone (THAHQ).
U.S. Pat. No. 3,073,680 uses a mixture of 2-ethylanthraquinone (EAQ) and 2-tetrahydroethylanthraquinone (THEAQ). However, it is impossible to increase the concentration of EAQ and THEAQ in the working solution because they have low solubility, which is directly related with the productivity of hydrogen peroxide.
U.S. Pat. No. 3,540,847 also uses EAQ and THEAQ as a working material. However, even though the proportion of THEAQ is higher than that of EAQ, the productivity of hydrogen peroxide is merely about 6.5-11 g per liter of the working solution.